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File Created: 24-Jul-1985 by BC Geological Survey (BCGS)
Last Edit:  12-May-2023 by Nicole Barlow (NB)

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NMI 094M9 Fsp1
Name TAM FLUORITE, TAM, LIARD FLUORSPAR, THOR Mining Division Liard
BCGS Map 094M060
Status Prospect NTS Map 094M09E
Latitude 059º 31' 59'' UTM 09 (NAD 83)
Longitude 126º 05' 06'' Northing 6603026
Easting 664843
Commodities Fluorite, Barite Deposit Types E11 : Carbonate-hosted fluorspar
E10 : Carbonate-hosted barite
Tectonic Belt Foreland Terrane Ancestral North America
Capsule Geology

The Tam fluorite deposit is located at the north end of Mould Creek, 13 kilometres north of the Liard River settlement on the Alaska Highway and approximately 200 kilometres west-northwest of Fort Nelson, BC. The deposit is situated at the southern extent of the Liard Plateau physiographic zone, and within the Foreland Belt of the Canadian Cordillera. Access to the property as of 2014 is via a privately owned and well-maintained gravel trail.

The regional geology is defined by the unconformable relationship between basement crystalline rocks of the North American Craton and the overlying, northwest-tapering wedge comprising the platformal sedimentary stratigraphy of the Western Canada Sedimentary Basin (Geological Survey of Canada Maps 46-1962, 1712A, 1713A). At a district scale, the Tam and related prospects are hosted in an open anticline with a gently south-plunging axis that defines the geometry of the Upper Devonian Besa River Formation and the Middle Devonian Dunedin Formation. The Tam prospect is one of several similar fluorite deposits, all hosted in a 17-kilometre-long belt defined by the unconformity between the Besa River and Dunedin Formations. All known fluorite deposits and prospects in the belt are situated at or proximal to the unconformity.

The Dunedin Formation consists of mid- to dark-grey, massive to thinly bedded fossiliferous limestone. It is generally exposed in the Teeter and Mould creek valleys, which are characterized by karst and 'mesa and butte' topography. The overlying Besa River Formation consists predominantly of black shale or slate and argillite, with some calcareous shale and minor, buff-brown dolomitic layers. The unconformity between the units is very irregular and characterized by extensive brecciation.

Fluorite deposits in this belt generally occur as lenticular replacement bodies or fracture infillings, predominantly in breccias of the underlying Dunedin limestone. In some instances, vein-type mineralization is also observed, along with replacement pods devoid of hostrock fragments and rare crustiform mineralization texture. The main mineralization occurs in breccias as partial to complete replacement of the hostrock and as breccia matrix. The breccias typically manifest with crackle, mosaic and chaotic textures. At the northern extent of the system, diamond drilling has revealed structural complexities: Fluorite-rich limestone breccia occurs above shale breccia, suggesting that the zone has been complexly deformed by thrusting or inverted by folding. If deformation is indeed stronger there, and structural brecciation is an important condition for mineralization, this area may have even more potential for mineralization (Assessment Report 3975).

The dominant ore minerals at the Tam showing are purple to black fluorite, calcite and witherite (BaCO3). Minor barytocalcite (BaCaCO3) and barite are also observed. Siliceous bands in the limestone may be relicts of original cherty layers. Fission-track studies of fluorite from the Gem prospect (MINFILE 094M 002), located 9 kilometres to the south, suggest that the age of the mineralization in the region is 332 ± 56 Ma; Open File 1992-16; Assessment Report 33580).

The mineralized zone of the Tam deposit extends north for at least 275 metres, varies between 50 and 165 metres in width and dips eastward, concordant with host stratigraphy. Hostrock brecciation proximal to the unconformity is inferred to be a primary control on mineralization. A chip sample of purple fluorite assayed 84.16 per cent calcium fluoride (Open File 1992-16, page 35). A sample of replacement and vein witherite with trace fluorite assayed 61.6 per cent barium oxide (Open File 1992-16). Some historical diamond drilling results are given in Geology, Exploration and Mining in British Columbia (1972), and additional composite metallurgical samples are provided in Assessment Report 33580. A semi-continuous channel sample taken at Tam trench 1 had a weighted average of 20.3 per cent calcium fluoride over 57.9 metres. Other notable trench samples include: 67.1 per cent calcium fluoride over 10.7 metres (trench 2) and 57.5 per cent calcium fluoride over 12.2 metres (trench 3; Assessment Report 33580). In 2012, a semi-continuous channel sample yielded 23.49 per cent calcium fluoride over 74.55 metres (McCallum, N.G. [2012-12-12]: Technical Report on the Liard Fluorspar Project). Historical calculated reserves by Conwest Exploration Co. Ltd., circa 1981, reported 2.4 million tonnes of 30 per cent calcium fluoride (Assessment Report 33580). The system is open to the north.

Fluorite mineralization at the Tam and related deposits is situated in a district of high structural complexity and, as such, multiple causative factors have been proposed. Sulphur isotope ratios recorded at barite deposits throughout northeastern BC indicate potential mixing of euxinic seawater with meteoric groundwater reserves, inducing low-temperature precipitation of barite in solution cavities (Morrow et al. 1978, in Assessment Report 33580); however, the Liard fluorspar system, including the Tam and related deposits, is isotopically and chemically unique relative to other systems in the region. A spatial and genetic link to the Robb Lake Mississippi Valley Type belt of mineralization has been proposed based on similar styles of carbonate-breccia-hosted infilling and replacement mineralization as well as similar fission-track age ranges, but this link has been refuted based on the lack of dolomitization, the lack of sulfides, and the disparity in fluorite mineralization between the Liard fluorspar and Robb Lake districts. A relationship to alkaline intrusive activity has also been proposed but supporting evidence is tenuous and conflicting. At present, the genetic history of the Liard fluorspar deposit belt is proposed to be influenced by multiple structural and fluid-flow events. Mississippian fluorite deposition is proposed to be the earliest and most significant mineralization event, and the much later Cretaceous-Paleogene Laramide orogeny is argued to have structurally influenced and redistributed fluorite mineralization (Assessment Report 33580).

Work History

In 1953, fluorite mineralization was discovered by Conwest Exploration at the GEM claims (MINFILE 094M 002) and a bulk sampling program was undertaken.

From 1971 to 1972, Conwest Exploration and Jorex Limited drilled approximately 60 diamond drill holes. Mineralized horizons measured between 10 to 20 metres thick, with between 10 to 50 per cent calcium fluoride (Assessment Report 33580).

In 1975, Jorex Limited and Conwest Exploration reported mineral reserves of 3.2 million tonnes at 32 per cent calcium fluoride (Assessment Report 34081).

In 1981, Conwest Exploration reported mineral reserves of 2.4 million tonnes at 30 per cent calcium fluoride (McCallum, N.G. [2012-12-12]: Technical Report on the Liard Fluorspar Project).

In 2012, Prima Fluorspar conducted channel and soil sampling programs on the Tam (MINFILE 094M 005), Tee (MINFILE 094M 010), Coral (MINFILE 094M 007) and Fire (MINFILE 094M 006) showings (Assessment Report 33580). Whole rock sample 380001 at Tam returned 51.0 per cent calcium fluoride; sample 380015 returned 65.6 per cent calcium fluoride. Both samples were hosted in limestone breccia. A semi-continuous composite channel sample returned 23.49 per cent calcium fluoride over 74.55 metres (Assessment Reports 33580, 34081).

In 2013, Prima Fluorspar conducted a gravity survey, along with mapping and bulk sampling programs. Sample Tam 1 returned 45 per cent fluorite over 11.0 metres; and sample Tam 2 returned 40 per cent fluorite over 11.0 metres (Assessment Report 34081).

Bibliography
EMPR ASS RPT 109, 1233, 3840, *3975, *33580, *34081, *34808
EMPR FIELDWORK 1988, pp. 478-479
EMPR GEM 1971-462; 1972-587
EMPR IND MIN FILE (Fluorite Occurrences in BC, (GEM) (in Ministry Library))
EMPR OF *1992-16, pp. 33-40
EMR MP CORPFILE (Conwest Exploration Company Limited; Jorex Limited)
GSC BULL 186
GSC MAP 46-1962; 1712A; 1713A
GSC P 72-32, p. 20
CJES, Vol. 15, pp. 1391-1406
N MINER, Vol. 57, No. 33, 1972
*McCallum, N.G. (2012-12-12): Technical Report on the Liard Fluorspar Project
EMPR PFD 675850, 675851

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